Current collection structure and electrochemical reaction cell stack for electrochemical reaction cell stack

Abstract

This suppresses the increase in resistance of the electrochemical reaction cell stack. [Solution] The current collector structure for an electrochemical reaction cell stack comprises a Cr-containing member and a Ni-containing member joined to the Cr-containing member, wherein the Ni-containing member is a polycrystalline material having multiple grain boundaries, and the proportion of grain boundaries with a grain boundary inclination angle of 0° or more and 40° or less is 5% or more and 45% or less.

Description

Technical Field

[0001] The technology disclosed in this specification relates to a current collector structure for an electrochemical reaction cell stack and an electrochemical reaction cell stack.

Background Art

[0002] As one of fuel cells that generate electricity by utilizing an electrochemical reaction between hydrogen and oxygen, a solid oxide fuel cell (hereinafter referred to as "SOFC") is known. SOFC is generally used in the form of a fuel cell stack. The fuel cell stack includes a single cell and a current collector structure for the fuel cell stack (hereinafter also simply referred to as "current collector structure"). The current collector structure is electrically connected to the single cell and collects the electric power generated in the single cell.

[0003] Conventionally, a current collector structure has been disclosed that includes an interconnector (Cr-containing member) formed of a ferritic stainless steel, which is an alloy containing Cr (chromium), and a fuel electrode side current collector (Ni-containing member) formed of Ni (nickel) and joined to the interconnector (for example, see Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] During the operation of the electrochemical reaction cell stack, inside the Ni-containing member, Cr diffusing from the Cr-containing member reacts with oxygen dissociated from H2O contained in the gas inside the electrochemical reaction cell stack, thereby growing an internal oxidation layer (for example, a layer containing Cr2O3 (chromium dioxide)). The growth of the internal oxidation layer may block the conductive path in the current collector structure and cause an increase in the resistance value of the electrochemical reaction cell stack.

[0006] Furthermore, these challenges are also common to current collection structures used in electrolytic cell stacks, which are a form of electrolytic cell (hereinafter referred to as "SOEC") that produces hydrogen using the electrolysis of water.In this specification, fuel cell single cells and electrolytic single cells are collectively referred to as electrochemical reaction single cells, and fuel cell stacks and electrolytic cell stacks are collectively referred to as electrochemical reaction cell stacks.In addition, these challenges are common not only to SOFCs and SOECs, but also to other types of electrochemical reaction cell stacks.

[0007] This specification discloses a technology capable of solving the above-mentioned problems. [Means for solving the problem]

[0008] The technologies disclosed herein can be implemented, for example, in the following forms:

[0009] (1) The current collector structure for an electrochemical reaction cell stack disclosed herein comprises a Cr-containing member containing Cr and a Ni-containing member joined to the Cr-containing member. In the current collector structure for an electrochemical reaction cell stack, the Ni-containing member is a polycrystalline material having a plurality of grain boundaries, and the proportion of grain boundaries among the plurality of grain boundaries having a grain boundary inclination angle of 0° or more and 40° or less is 5% or more and 45% or less. According to this current collector structure for an electrochemical reaction cell stack, since the Ni-containing member is a polycrystalline material having a plurality of grain boundaries, and the proportion of grain boundaries among the plurality of grain boundaries having a grain boundary inclination angle of 0° or more and 40° or less is 5% or more and 45% or less, it is possible to suppress the increase in the resistance value of the electrochemical reaction cell stack.

[0010] (2) In the current collection structure for the electrochemical reaction cell stack described above, the proportion of grain boundaries among the plurality of grain boundaries in which the grain boundary inclination angle is 50° or more and 90° or less may be 5% or more and 45% or less. With this configuration, furthermore, since the proportion of grain boundaries among the plurality of grain boundaries in which the grain boundary inclination angle is 5% or more and 45% or less may be 5%, the increase in the resistance value of the electrochemical reaction cell stack can be suppressed.

[0011] (3) In the current collector structure for the electrochemical reaction cell stack described above, the thickness of the Ni-containing member may be 1.5 times or more the average particle diameter of the Ni crystal grains forming the polycrystalline body. With this configuration, furthermore, because the thickness of the Ni-containing member is 1.5 times or more the average particle diameter of the Ni crystal grains, both ends of the grain boundary on one surface do not reach both surfaces of the Ni-containing member, thereby suppressing an increase in the resistance value of the electrochemical reaction cell stack.

[0012] (4) The electrochemical reaction cell stack may be configured to include a single cell having an electrolyte layer, an air electrode disposed on one side of the electrolyte layer, and a fuel electrode disposed on the other side of the electrolyte layer, and a current collector structure for the electrochemical reaction cell stack, wherein the current collector structure for the electrochemical reaction cell stack and the single cell are electrically connected. With this configuration, in the electrochemical reaction cell stack, further intrusion of oxygen into the Ni-containing member of the current collector structure for the electrochemical reaction cell stack is suppressed, thereby suppressing the growth of the internal oxide layer in the Ni-containing member and suppressing an increase in the resistance value of the electrochemical reaction cell stack.

[0013] (5) In the electrochemical reaction cell stack described above, the Ni-containing member may be placed in the fuel chamber facing the fuel electrode. With this configuration, further oxygen intrusion into the Ni-containing member of the electrochemical reaction cell stack current collector structure placed in the fuel chamber is suppressed, thereby suppressing the growth of the internal oxide layer in the Ni-containing member and preventing an increase in the resistance value of the electrochemical reaction cell stack.

[0014] Note that the technology disclosed in this specification can be implemented in various forms. For example, it can be implemented in the form of a current collector structure for an electrochemical reaction cell stack, an interconnector-electrochemical reaction single cell composite having a single cell and a current collector structure for an electrochemical reaction cell stack, an electrochemical reaction cell stack, and a method for manufacturing a current collector structure for an electrochemical reaction cell stack, etc.

Brief Description of the Drawings

[0015] [Figure 1] Perspective view showing the appearance of a fuel cell stack [Figure 2] Explanatory drawing showing the XZ cross-section of the fuel cell stack at the position II-II of FIG. 1 [Figure 3] Explanatory drawing showing the XZ cross-section of the fuel cell stack at the position III-III of FIG. 1 [Figure 4] Explanatory drawing showing the XZ cross-section of two adjacent power generation units at the same position as the cross-section shown in FIG. 2 [Figure 5] Explanatory drawing showing the XZ cross-section of two adjacent power generation units at the same position as the cross-section shown in FIG. 3 [Figure 6] Cross-sectional view showing details of the current collector structure of the embodiment [Figure 7] Explanatory drawing showing the cross-section of the current collector structure after operation [Figure 8] Explanatory drawing showing the cross-section of the current collector structure after operation [Figure 9] Explanatory drawing showing the performance evaluation test (deterioration rate) in a graph

Modes for Carrying Out the Invention

[0016] A. Embodiment: A-1. Configuration of the fuel cell stack 10 FIG. 1 is a perspective view showing the appearance of the fuel cell stack 10, FIG. 2 is an explanatory view showing the XZ cross-section of the fuel cell stack 10 at the position II-II in FIG. 1, and FIG. 3 is an explanatory view showing the XZ cross-section of the fuel cell stack 10 at the position III-III in FIG. 1. In each figure, XYZ axes orthogonal to each other for specifying directions are shown. In this specification, for convenience, the Z-axis direction is referred to as the vertical direction, the positive Z-axis direction is referred to as the upward direction, and the negative Z-axis direction is referred to as the downward direction. However, the fuel cell stack 10 may actually be installed in a direction different from such a direction. Further, the "thickness" of each member in this specification means the length of each member in the vertical direction (Z-axis direction) unless otherwise specified. The fuel cell stack 10 is an example of an electrochemical reaction cell stack.

[0017] As shown in FIGS. 1 to 3, the fuel cell stack 10 includes a power generation block 100, a terminal separator 230, a first plate 232, a second plate 260, a first terminal plate 240, a second terminal plate 250, an insulating portion 220, a first end plate 210, a second end plate 270, and four gas passage members 280. The first end plate 210, the insulating portion 220, the terminal separator 230, the first terminal plate 240, the power generation block 100, the second terminal plate 250, the second plate 260, and the second end plate 270 have substantially the same-sized rectangular outer shapes and are arranged to overlap in this order in a predetermined arrangement direction (vertical direction).

[0018] As shown in FIG. 1, the fuel cell stack 10 has bolt holes BH penetrating from the first end plate 210 to the second end plate 270 near each of the four corners. Bolts B are inserted into each bolt hole BH. Nuts N are screwed to both ends of each bolt B. These bolts B and nuts N integrally fasten the members from the first end plate 210 to the second end plate 270. As shown in FIGS. 2 and 3, the first plate 232 is supported by the terminal separator 230. The four gas passage members 280 are connected to the second end plate 270.

[0019] As shown in Figures 2 and 3, the power generation block 100 is composed of a plurality (seven in this embodiment) of power generation units 100U arranged in a predetermined arrangement direction (vertical direction).

[0020] The first end plate 210 is a member formed by press-forming (bending) a single plate-shaped member, and is made of a conductive material such as stainless steel. As shown in Figures 1 to 3, the first end plate 210 comprises a rectangular frame-shaped planar portion 211 having a through hole 212 near the center, and an outer projection 213 and an inner projection 214 that project from the planar portion 211 in the opposite direction to the insulating portion 220 (upwards in Figure 2). The planar portion 211 has holes that constitute the bolt holes BH described above. The outer projection 213 protrudes from the outer peripheral edge of the planar portion 211. The outer projection 213 is formed around the entire circumference of the outer peripheral portion of the planar portion 211. The inner projection 214 protrudes from the inner peripheral edge of the planar portion 211. The inner projection 214 is formed around the entire circumference of the inner peripheral portion of the planar portion 211.

[0021] The insulating portion 220 is a rectangular frame-shaped member having a through hole near the center, and is formed of, for example, an insulating material. As shown in Figures 2 and 3, the insulating portion 220 is sandwiched between the first end plate 210 and the end separator 230, thereby ensuring insulation between the first end plate 210 and the end separator 230.

[0022] As shown in Figures 2 and 3, the end separator 230 is a rectangular frame-shaped member having a through hole 231 near the center, and is made of, for example, metal.

[0023] The first plate 232 is a rectangular, flat member made of a conductive material such as stainless steel. As shown in Figures 2 and 3, the first plate 232 is joined to the peripheral portion of the through hole 231 in the end separator 230, for example, by welding. The end separator 230 and the first plate 232 separate the power generation block 100 from the external space of the fuel cell stack 10.

[0024] The first plate 232 is connected to an interconnector 190, described later, provided on a power generation unit 100U located at one end (the upper end in Figure 2) of the multiple power generation units 100U that make up the power generation block 100, via a connecting member having the same structure as the fuel electrode current collector 144, described later. In this way, the power generation unit 100U and the first plate 232 are electrically connected.

[0025] The first terminal plate 240 is a rectangular frame-shaped member having a through hole 241 near the center, and is made of a conductive material such as ferritic stainless steel that forms an alumina oxide film on its surface. The first terminal plate 240 is electrically connected to a power generation unit 100U located at one end (upper end in Figure 2) of the multiple power generation units 100U that make up the power generation block 100, via the first plate 232 and the end separator 230. One end of the first terminal plate 240 (right end in Figure 2) protrudes laterally from the power generation block 100, and this protruding portion functions as the positive output terminal of the fuel cell stack 10.

[0026] The second terminal plate 250 is a rectangular plate-shaped member, formed from a conductive material such as ferritic stainless steel that forms an alumina oxide film on its surface. The second terminal plate 250 is electrically connected to the power generation unit 100U located at the other end (lower end in Figure 2) of the multiple power generation units 100U that make up the power generation block 100. One end of the second terminal plate 250 (right end in Figure 2) protrudes laterally from the power generation block 100, and this protruding portion functions as the negative output terminal of the fuel cell stack 10.

[0027] The second plate 260 is a rectangular, flat member, formed of, for example, an insulating material. The peripheral edge of the second plate 260 is sandwiched between the second terminal plate 250 and the second end plate 270, thereby ensuring insulation between the second terminal plate 250 and the second end plate 270.

[0028] The second end plate 270 is a member formed by press-forming (bending) a single plate-shaped member, and is made of a conductive material such as stainless steel. The second end plate 270 comprises a rectangular frame-shaped planar portion 271 having a through hole 272 near the center, and an outer projection 273 and an inner projection 274 projecting from the planar portion 271 in the opposite direction to the second terminal plate 250 (downward in Figure 2). The planar portion 271 has holes that constitute the bolt holes BH described above. The outer projection 273 protrudes from the outer peripheral edge of the planar portion 271. The outer projection 273 is formed around the entire circumference of the outer peripheral portion of the planar portion 271. The inner projection 274 protrudes from the inner peripheral edge of the planar portion 271. The inner projection 274 is formed around the entire circumference of the inner peripheral portion of the planar portion 271.

[0029] As shown in Figures 1 to 3, the fuel cell stack 10 has four holes that penetrate from the power generation block 100 to the second end plate 270. The four holes are the oxidizer gas supply manifold 311, the oxidizer gas discharge manifold 312, the fuel gas supply manifold 321, and the fuel gas discharge manifold 322, respectively.

[0030] As shown in Figure 2, the oxidizer gas supply manifold 311 is a gas flow path that supplies oxidizer gas OG, introduced from outside the fuel cell stack 10, to the air chambers 313 of each power generation unit 100U (described later). The oxidizer gas discharge manifold 312 is a gas flow path that discharges oxidizer off-gas OOG, discharged from the air chambers 313 of each power generation unit 100U, to the outside of the fuel cell stack 10. For example, air is used as the oxidizer gas OG. The oxidizer gas supply manifold 311 and the oxidizer gas discharge manifold 312 are located on opposite sides of the air chamber 313.

[0031] As shown in Figure 3, the fuel gas supply manifold 321 is a gas passage that supplies fuel gas FG introduced from outside the fuel cell stack 10 to the fuel chamber 323 of each power generation unit 100U, which will be described later. The fuel gas discharge manifold 322 is a gas passage that discharges fuel off-gas FOG discharged from the fuel chamber 323 of each power generation unit 100U to the outside of the fuel cell stack 10. As the fuel gas FG, for example, hydrogen-rich gas obtained by reforming city gas is used. The fuel gas supply manifold 321 and the fuel gas discharge manifold 322 are located on opposite sides of the fuel chamber 323.

[0032] Each of the four gas passage members 280 comprises a main body portion 281 and a flange portion 282, as shown in Figures 1 to 3. The main body portion 281 has a gas through-hole 283 that penetrates vertically. The flange portion 282 is provided so as to protrude outward from the other end of the main body portion 281 (the lower end in Figures 2 and 3). The flange portion 282 has a plurality of bolt holes 284. Bolts (not shown) for connecting the fuel cell stack 10 to an external device are inserted into each bolt hole 284. One end of the main body portion 281 provided on the four gas passage members 280 (the upper end in Figures 2 and 3) is joined to the second end plate 270, for example by welding, and the gas through-holes 283 communicate with manifolds 311, 312, 321, and 322, respectively. Gas piping (not shown) for gas supply or discharge is connected to each main body portion 281.

[0033] Figure 4 is an explanatory diagram showing the XZ cross-sections of two adjacent power generation units 100U at the same location as the cross-section shown in Figure 2. Figure 5 is an explanatory diagram showing the XZ cross-sections of two adjacent power generation units 100U at the same location as the cross-section shown in Figure 3. As shown in Figures 4 and 5, the power generation unit 100U comprises a single cell 110, a single cell separator 120, an air electrode frame 130, a fuel electrode frame 140, a current collection structure 160, and two IC separators 180. One IC separator 180, the air electrode frame 130, the single cell separator 120, the fuel electrode frame 140, and the other IC separator 180 are arranged in this order, overlapping each other.

[0034] The single cell 110 comprises an electrolyte layer 112, an air electrode 114, a fuel electrode 116, and a reaction prevention layer 118. As shown in Figures 4 and 5, the air electrode 114, the reaction prevention layer 118, the electrolyte layer 112, and the fuel electrode 116 are arranged in this order. The single cell 110 in this embodiment is a fuel electrode-supported single cell in which the other layers constituting the single cell 110 (electrolyte layer 112, air electrode 114, and reaction prevention layer 118) are supported by the fuel electrode 116. The single cell 110 is supported by a single cell separator 120.

[0035] The electrolyte layer 112 is a rectangular, flat member having one side on which the air electrode 114 is located (the upper side in Figures 4 and 5) and another side parallel to the air electrode 116 (the lower side in Figures 4 and 5). The electrolyte layer 112 is a layer containing a solid oxide (e.g., YSZ (yttria-stabilized zirconia)). The air electrode 114 is a layer having a rectangular shape smaller than the electrolyte layer 112 and contains, for example, a perovskite-type oxide (e.g., LSCF (lanthanum strontium cobalt iron oxide)). The fuel electrode 116 is a layer having a rectangular shape approximately the same size as the electrolyte layer 112 and contains, for example, Ni, a cermet made of Ni and ceramic particles, a Ni-based alloy, etc. The reaction prevention layer 118 is a layer having a rectangular shape approximately the same size as the air electrode 114 and contains, for example, GDC (gadolinium-doped ceria). The reaction prevention layer 118 has the function of suppressing the reaction of elements diffused from the air electrode 114 (e.g., Sr (strontium)) with elements contained in the electrolyte layer 112 (e.g., Zr (zirconium)) to produce a highly resistive material (e.g., SrZrO3 (strontium zirconate)).

[0036] As shown in Figures 4 and 5, the single-cell separator 120 is a rectangular frame-shaped member having a substantially rectangular through-hole 121 near the center, and is made of, for example, metal. The periphery of the through-hole 121 in the single-cell separator 120 is joined to the periphery of one surface of the electrolyte layer 112 (the surface on which the air electrode 114 is located: the upper surface in Figures 4 and 5) by a joint 124. The joint 124 is made of, for example, brazing material (Ag brazing).

[0037] As shown in Figures 4 and 5, the air electrode frame 130 is a rectangular frame-shaped member having a substantially rectangular through hole 131 near the center, and is formed of, for example, mica. As shown in Figure 4, the air electrode frame 130 has an oxidant gas supply communication channel 132 that connects the oxidant gas supply manifold 311 and the air chamber 313, and an oxidant gas discharge communication channel 133 that connects the air chamber 313 and the oxidant gas discharge manifold 312.

[0038] As shown in Figures 4 and 5, the fuel electrode frame 140 is a rectangular frame-shaped member having a substantially rectangular through hole 141 near the center, and is made of, for example, metal. As shown in Figure 5, the fuel electrode frame 140 has a fuel gas supply communication passage 142 that connects the fuel gas supply manifold 321 and the fuel chamber 323, and a fuel gas discharge communication passage 143 that connects the fuel chamber 323 and the fuel gas discharge manifold 322.

[0039] As shown in Figures 4 and 5, the IC separator 180 is a rectangular frame-shaped member having a through hole 181 near the center, and is made of, for example, metal.

[0040] The current collection structure 160 is electrically connected to the single cell 110 and collects the power generated by the single cell 110. The current collection structure 160 comprises an interconnector 190 and a fuel electrode current collector member 144. The current collection structure 160 is an example of a current collection structure for an electrochemical reaction cell stack. The interconnector 190 is an example of a Cr-containing material. The fuel electrode current collector member 144 is an example of a Ni-containing material.

[0041] As shown in Figures 4 and 5, the interconnector 190 comprises a rectangular flat plate portion 191, a plurality of plate-shaped air electrode current collectors 192 protruding from one surface of the flat plate portion 191 toward the air electrode 114, and a coating layer 193. The flat plate portion 191 and the air electrode current collectors 192 are formed of an alloy containing Fe and Cr (for example, ferritic stainless steel) and are conductive. The coating layer 193 is conductive and is arranged to cover the surface of the air electrode current collectors 192 and the surface of the flat plate portion 191 on which the air electrode current collectors 192 are arranged. The flat plate portion 191 is joined to the periphery of the through hole 181 in the IC separator 180, for example, by welding. The interconnector 190 is supported by the IC separator 180.

[0042] The fuel electrode current collector 144 is a member that connects the interconnector 190 and the fuel electrode 116. As shown in Figures 4 and 5, the fuel electrode current collector 144 comprises an interconnector-facing portion 146, an electrode-facing portion 145 parallel to the interconnector-facing portion 146, and a connecting portion 147 that connects the electrode-facing portion 145 and the interconnector-facing portion 146, and is generally U-shaped. The electrode-facing portion 145 is joined to the fuel electrode 116, and the interconnector-facing portion 146 is joined to the flat plate portion 191 of the interconnector 190. The fuel electrode current collector 144 is positioned between the single cell 110 and the interconnector 190. The fuel electrode current collector 144 will be described in detail later.

[0043] As shown in Figures 4 and 5, the interconnector 190 is shared by two adjacent power generation units 100U. More specifically, as shown in Figures 4 and 5, the air electrode current collector 192 is joined to the air electrode 114 of a single cell 110 provided in one of the two adjacent power generation units 100U via a conductive bonding material 196 made of, for example, a spinel-type oxide, thereby electrically connecting to the air electrode 114. The flat plate portion 191 is electrically connected to the fuel electrode 116 of a single cell 110 provided in the other of the two adjacent power generation units 100U via a fuel electrode current collector 144. This ensures electrical conductivity between the two adjacent power generation units 100U.

[0044] However, as shown in Figure 2, the power generation unit 100U located at the other end (the lower end in Figure 2) among the multiple power generation units 100U does not have an interconnector 190 on the fuel electrode 116 side. The fuel electrode 116 provided in this power generation unit 100U is connected to the second terminal plate 250 via a fuel electrode current collector 144.

[0045] A spacer 149, for example made of mica, is placed between the electrode facing portion 145 and the interconnect facing portion 146. As a result, the fuel electrode current collector 144 follows the deformation of the power generation unit 100U due to temperature cycles and reaction gas pressure fluctuations, and the electrical connection between the fuel electrode 116 and the interconnect 190 (or second terminal plate 250) via the fuel electrode current collector 144 is maintained in good condition.

[0046] As shown in Figures 4 and 5, the space partitioned by the single-cell separator 120 and single cell 110, the air electrode frame 130, the IC separator 180 and interconnector 190 faces the air electrode 114 and forms an air chamber 313 through which the oxidizer gas OG flows. The air electrode frame 130 partitions the air chamber 313 from the outside space around its entire circumference and seals the space between the single-cell separator 120 and the IC separator 180, preventing gas from leaking from the air chamber 313 into the outside space.

[0047] Furthermore, the space partitioned by the single-cell separator 120 and single cell 110, the fuel electrode frame 140, the IC separator 180 and interconnector 190 faces the fuel electrode 116 and forms a fuel chamber 323 through which fuel gas FG flows. The fuel electrode frame 140 partitions the fuel chamber 323 from the outside space around its entire circumference and seals the space between the single-cell separator 120 and the IC separator 180, preventing gas from leaking from the fuel chamber 323 into the outside space.

[0048] The single-cell separator 120 separates the air chamber 313 from the fuel chamber 323, suppressing gas leakage (cross-leakage) from the air electrode 114 to the fuel electrode 116, or from the fuel electrode 116 to the air electrode 114, around the single cell 110. In addition, the IC separator 180 and interconnector 190 suppress gas leakage between adjacent power generation units 100U.

[0049] (Operation of fuel cell stack 10) As shown in Figures 2 and 4, the oxidizer gas OG is supplied to the oxidizer gas supply manifold 311 via gas piping (not shown) and gas passage member 280, and then supplied to the air chamber 313 via the oxidizer gas supply communication channel 132.

[0050] Furthermore, as shown in Figures 3 and 5, the fuel gas FG is supplied to the fuel gas supply manifold 321 via gas piping (not shown) and gas passage members 280, and then supplied to the fuel chamber 323 via the fuel gas supply communication channel 142.

[0051] When oxidant gas OG is supplied to the air chamber 313 of each power generation unit 100U and fuel gas FG is supplied to the fuel chamber 323, electricity is generated in the single cell 110 by an electrochemical reaction between the oxidant gas OG and fuel gas FG. This power generation reaction is an exothermic reaction. As described above, the interconnector 190 is shared by two adjacent power generation units 100U, and the interconnector 190 ensures conductivity between the two adjacent power generation units 100U. In other words, the multiple power generation units 100U included in the fuel cell stack 10 are electrically connected in series. Furthermore, the power generation unit 100U located at the other end (lower end in Figure 2) of the multiple power generation units 100U is electrically connected to the second terminal plate 250, and the power generation unit 100U located at the one end (upper end in Figure 2) is electrically connected to the first terminal plate 240. As a result, the electrical energy generated in each power generation unit 100U is extracted from the terminal plates 240 and 250, which function as output terminals of the fuel cell stack 10. Since SOFCs generate electricity at relatively high temperatures (for example, 700°C to 1000°C), the fuel cell stack 10 may be heated by a heater (not shown) after startup until the high temperature can be maintained by the heat generated by power generation.

[0052] As shown in Figures 2 and 4, the oxidizer off-gas OOG discharged from the air chamber 313 of each power generation unit 100U to the oxidizer gas discharge manifold 312 via the oxidizer gas discharge communication channel 133 is discharged to the outside of the fuel cell stack 10 through the internal space of the main body 281. Also, as shown in Figures 3 and 5, the fuel off-gas FOG discharged from the fuel chamber 323 of each power generation unit 100U to the fuel gas discharge manifold 322 via the fuel gas discharge communication channel 143 is discharged to the outside of the fuel cell stack 10 through the internal space of the main body 281.

[0053] A-2. Details of the current collection structure 160 Figure 6 is a cross-sectional view showing details of the current collector structure 160 of the embodiment. Figure 6 is an enlarged view of the X1 portion of Figure 5. Figure 6 shows the interconnector 190, the fuel electrode current collector member 144, and the bonding region CP. The bonding region CP is the area where the interconnector 190 and the fuel electrode current collector member 144 are in physical contact. Here, physical contact means, for example, that there is no gap of 1 μm or more between the interconnector 190 and the fuel electrode current collector member 144. The fuel electrode current collector member 144 has a surface S1 which is not bonded to the interconnector 190, and a surface S2 which is bonded to the interconnector 190.

[0054] As shown in Figure 6, the fuel electrode current collector 144 is formed of a foil containing Ni (hereinafter referred to as "Ni foil"). The fuel electrode current collector 144 is formed by shaping the Ni foil into a U-shape to form an electrode facing portion 145, an interconnector facing portion 146, and a connecting portion 147 (see Figure 5). The thickness L1 of the Ni foil may be 2 μm or more and 100 μm or less, or 20 μm or more and 50 μm or less.

[0055] (Composition of fuel electrode current collector 144) The Ni content of the fuel electrode current collector 144 may be, for example, 90% by mass or more, or 95% by mass. The fuel electrode current collector 144 may contain other substances in addition to Ni. For example, the fuel electrode current collector 144 may contain one of Ti, Al, Mn, Si, and Mg (hereinafter referred to as "specific elements"), or it may contain two or more of the specific elements. The specific elements may be contained in the fuel electrode current collector 144 in an amount of 0.0001% by mass or more and 1% by mass or less. Furthermore, the specific elements may be contained in the fuel electrode current collector 144 not only as individual elements, but also as compounds such as oxides of the specific elements. In addition, the fuel electrode current collector 144 may contain Cr in addition to the specific elements. One example is that, due to the operation of the fuel cell stack 10, Cr contained in the interconnector 190 diffuses into the fuel electrode current collector 144, resulting in Cr being contained in the fuel electrode current collector 144.

[0056] (Ni crystal grains of fuel electrode current collector 144) As shown in Figure 6, the fuel electrode current collector 144 of this embodiment is a polycrystalline material (hereinafter referred to as "Ni polycrystalline material") formed by a plurality of Ni crystal grains (hereinafter referred to as "Ni crystal grains"). The term "crystal" here includes not only single crystals but also twinned crystals. The degree of crystallinity of the Ni polycrystalline material may be 90% by mass or more, or 95% by mass or more.

[0057] (Grain boundaries in polycrystalline Ni) In a Ni polycrystalline material, any two adjacent Ni crystal grains are designated as the first Ni crystal grain and the other as the second Ni crystal grain. The boundary between the first Ni crystal grain and the second Ni crystal grain is the grain boundary. For example, as shown in Figure 6, the boundary between adjacent Ni crystal grains CA and CB is the grain boundary B0. The first Ni crystal grain and the second Ni crystal grain each have a crystal orientation. The grain boundary inclination angle of the grain boundary between the first Ni crystal grain and the second Ni crystal grain is calculated from the crystal orientation of the first Ni crystal grain and the crystal orientation of the second Ni crystal grain. Of all the grain boundaries present in a Ni polycrystalline material, the abundance ratio of the first grain boundary is 5% or more and 40% or less (hereinafter, the ratio of grain boundaries with a specific range of grain boundary inclination angles to the total number of grain boundaries in a Ni polycrystalline material is referred to as the "abundance ratio"). The first grain boundary is a grain boundary with a grain boundary inclination angle of 0° or more and 40° or less. Furthermore, the abundance ratio of the second grain boundary may be between 5% and 45%. The second grain boundary is a grain boundary with a grain boundary inclination angle of 50° to 90°.

[0058] The above details are explained in Figures 7 and 8. Figures 7 and 8 are explanatory diagrams showing a cross-section of the current collection structure 160 after continuous operation of the fuel cell stack 10. Figures 7 and 8 are enlarged views of the X2 portion of Figure 6. Figure 7 is a schematic diagram of a scanning electron microscope (SEM) image (hereinafter referred to as "SEM image") showing a cross-section of the current collection structure 160. The crystal structure of each component shown in Figure 7 only shows polycrystalline Ni. Figure 8 is a schematic diagram of the schematic diagram in Figure 7, where pixels containing 50% or more of the element Cr out of the total elements excluding oxygen are mapped onto Figure 7. Note that Figures 7 and 8 are schematic diagrams for explaining the current collection structure 160 and do not represent a specific field of view of a specific fuel cell stack 10.

[0059] As shown in Figures 7 and 8, when the fuel cell stack 10 is operated continuously, the Ni polycrystalline fuel electrode current collector 144 forms a first internal oxide layer CO1 upwards and a second internal oxide layer CO2 downwards (hereinafter, the first internal oxide layer CO1 and the second internal oxide layer CO2 downwards are collectively referred to as "internal oxide layer CO"). The internal oxide layer CO is formed of Cr2O3.

[0060] Furthermore, as shown in Figures 7 and 8, continuous operation of the fuel cell stack 10 causes penetration areas E1 to E4 (collectively referred to as "penetration areas E") to form in the Ni polycrystalline material. Penetration areas E1 to E4 penetrate from grain boundary B1 to grain boundary B4. Penetration areas E are formed of Cr2O3. Penetration areas E extend from the first internal oxide layer CO1 into the interior of the Ni polycrystalline material. In particular, penetration area E2 penetrates deeper into the Ni polycrystalline material than the other penetration areas E. The depth L3 of penetration area E2 (distance from the surface S1 of the Ni polycrystalline material to the tip of penetration area E2) is 1 / 4 or more of the thickness L1 of the Ni polycrystalline material (specifically, about 12 μm). On the other hand, penetration areas E1, E3, and E4 do not penetrate deeply into the interior of the Ni polycrystalline material.

[0061] Table 1 shows the grain boundary inclination angles of the grain boundaries (grain boundaries B1 to grain boundaries B7) appearing on the surface S1 of the Ni polycrystalline material in Figure 7. [Table 1]

[0062] As shown in Table 1, the grain boundary inclination angle of grain boundary B2 corresponding to the intrusion area E2 is 45°. On the other hand, the grain boundary inclination angles of grain boundaries B1, B3, and B4 that form the other intrusion areas E are 25°, 25°, and 40°, respectively. On the other hand, no intrusion into the Ni polycrystalline material was observed at grain boundaries B5, B6, and B7 (see Figure 8). The grain boundary inclination angles of grain boundaries B5, B6, and B7 are 57°, 50°, and 60°, respectively. As a result, intrusion into the Ni polycrystalline material is more pronounced at grain boundaries where the grain boundary inclination angle is around 45°, that is, where the grain boundary inclination angle is greater than 40° and less than 50°. In other words, erosion of the fuel electrode current collector member 144, which is a Ni polycrystalline material having grain boundaries with a grain boundary inclination angle greater than 40° and less than 50°, is more pronounced.

[0063] (Size of Ni crystal grains) The size of the Ni crystal grains forming the Ni polycrystalline material is as follows: The thickness L1 of the Ni polycrystalline material may be 1.5 times or more the average particle diameter based on the number of Ni crystal grains, or 2 times or more (see Figure 6). The average particle diameter based on the number of Ni crystal grains may be, for example, 35 μm or less, 25 μm or less, or 15 μm or less. In addition, the length L2 of the Ni crystal grains in the vertical direction (Z-axis direction) may, on average, be 2 / 3 times or less the thickness L1 of the Ni polycrystalline material, or 1 / 2 times or less. The average length L2 of the Ni crystal grains in the vertical direction (Z-axis direction) may be 35 μm or less, 25 μm or less, or 15 μm or less.

[0064] (Analysis methods for polycrystalline materials) The grain boundary inclination angle of the grain boundary formed between the first Ni crystal grain and the second Ni crystal grain adjacent to the first Ni crystal grain, as well as the particle diameter and vertical length of the Ni crystal grain, are calculated, for example, using a device equipped with a focused ion beam (FIB) on a scanning electron microscope (SEM) (FIB-SEM) and an electron backscatter diffraction (EBSD) detector. Specifically, the current collector structure 160 is cut in the Z-axis direction so as to include the junction region CP between the fuel electrode current collector member 144 and the interconnector 190, and the region where the fuel electrode current collector member 144 and the interconnector 190 are not joined. After embedding the cut current collector structure 160 in epoxy resin, the cut surface of the current collector structure 160 is polished (hereinafter, the polished cut surface of the current collector structure 160 is referred to as the "SEM sample"). Then, the cut surface is treated with FIB. Subsequently, SEM image data of the cross-section of the current collector structure 160, magnified 1000 times, is obtained using SEM. The SEM is adjusted so that at 1000x magnification, more than 10 Ni crystal grains in the Ni polycrystalline material can be seen in the image. Furthermore, crystal orientation map data of the Ni polycrystalline material is obtained from the FIB-treated SEM sample using an EBSD detector. From the SEM image data and crystal orientation map data, grain boundaries of the Ni polycrystalline material are detected, and the crystal orientation of each Ni crystal grain is calculated. The grain boundary inclination angle of each grain boundary is calculated from the detected grain boundary data of the Ni polycrystalline material and the calculated crystal orientation data of each Ni crystal grain. In addition, the particle diameter and vertical length of the Ni crystal grains are calculated from the detected grain boundary data of the Ni polycrystalline material. The particle diameter of the Ni crystal grains is measured using a general method. Specifically, the particle size is calculated by determining the area of ​​the Ni crystal grain from the detected grain boundary data of the Ni polycrystalline material, and then determining the particle size of the Ni crystal grain by the diameter of a circle with the same area.

[0065] (Manufacturing method for current collection structure 160) The method for manufacturing the current collector structure 160 is as follows. First, the Ni foil, which is the fuel electrode current collector 144, is formed by known methods such as rolling or electrolysis. Then, the Ni foil is subjected to a heat treatment, and the proportion of first grain boundaries is adjusted to be between 5% and 45% by adjusting the temperature and time of the heat treatment. Specifically, the rolled Ni foil is heat-treated in an airtight environment. The heat treatment is carried out in a vacuum environment created by replacing the air with argon gas and then removing the argon gas. The heat treatment temperature may be 700°C to 1000°C or 850°C to 950°C. The heat treatment time may be 15 minutes to 180 minutes or 20 minutes to 60 minutes (hereinafter referred to as the "Ni foil pretreatment process").

[0066] Next, the interconnector 190 manufactured by a known method and the fuel electrode current collector 144 formed from previously manufactured Ni foil are joined. Specifically, the interconnector 190 and the fuel electrode current collector 144 are joined by holding them at a temperature of, for example, 850°C for 3 hours under an oxygen partial pressure equal to or greater than the oxygen partial pressure at which Ni is oxidized to NiO. The oxygen partial pressure at which Ni is oxidized to NiO can be determined, for example, from the Ellingham diagram. The type of gas is not particularly limited as long as the oxygen partial pressure is equal to or greater than the oxygen partial pressure at which Ni is oxidized to NiO (hereinafter referred to as the "joining process").

[0067] Next, the interconnector 190 and the fuel electrode current collector 144 are heated in a hydrogen gas atmosphere (800-900°C for 3 hours). This reduces the NiO that was oxidized during the joining of the interconnector 190 and the fuel electrode current collector 144 back to Ni (hereinafter referred to as the "reduction process").

[0068] A-3. Effects of this embodiment As described above, the current collector structure 160 of this embodiment comprises an interconnector 190 containing Cr and a fuel electrode current collector member 144 containing Ni that is joined to the interconnector 190. In the current collector structure 160, the fuel electrode current collector member 144 is a polycrystalline material having multiple grain boundaries. Of the multiple grain boundaries, the proportion of grain boundaries with a grain boundary inclination angle of 0° or more and 40° or less (first grain boundaries) is 5% or more and 45% or less. According to the current collector structure 160 of this embodiment, the fuel electrode current collector member 144 is a polycrystalline material having multiple grain boundaries, and of the multiple grain boundaries, the proportion of first grain boundaries is 5% or more and 45% or less, so that the increase in the resistance value of the fuel cell stack 10 can be suppressed.

[0069] In the current collection structure 160 of this embodiment, the proportion of grain boundaries (second grain boundaries) with a grain boundary inclination angle of 50° or more and 90° or less among the plurality of grain boundaries may be set to 5% or more and 45% or less. As a result, since the proportion of second grain boundaries among the plurality of grain boundaries is 5% or more and 45% or less, an increase in the resistance value of the fuel cell stack 10 can be suppressed.

[0070] In the current collector structure 160 of this embodiment, the thickness L1 of the fuel electrode current collector 144 may be configured to be 1.5 times or more the average particle diameter of the Ni crystal grains forming the polycrystalline material. As a result, since the thickness of the fuel electrode current collector 144 is 1.5 times or more the average particle diameter of the Ni crystal grains, the ends of the grain boundaries on one surface do not reach both surfaces of the fuel electrode current collector 144, thereby suppressing an increase in the resistance value of the fuel cell stack 10.

[0071] In the fuel cell stack 10 of this embodiment, a single cell 110 having an electrolyte layer 112, an air electrode 114 disposed on one side of the electrolyte layer 112, and a fuel electrode 116 disposed on the other side of the electrolyte layer 112, and a current collector structure 160 may be provided, and the current collector structure 160 and the single cell 110 may be electrically connected. As a result, further intrusion of oxygen into the fuel electrode current collector member 144 is suppressed in the current collector structure 160, thereby suppressing the growth of the internal oxide layer CO in the fuel electrode current collector member 144 and suppressing the increase in the resistance value of the fuel cell stack 10.

[0072] In the fuel cell stack 10 of this embodiment, the fuel electrode current collector 144 may be placed in the fuel chamber 323 facing the fuel electrode 116. This suppresses further oxygen intrusion into the fuel electrode current collector 144 within the current collector structure 160 placed in the fuel chamber 323, thereby suppressing the growth of the internal oxide layer CO in the fuel electrode current collector 144 and preventing an increase in the resistance value of the fuel cell stack 10.

[0073] A-4. Performance Evaluation Next, the performance evaluation of this embodiment will be described. Various current collector structures 160 were prepared, each formed from Ni foil with different physical properties. Samples of fuel cell stacks 10 (SA1 to SA8) equipped with each current collector structure 160 were fabricated, and the performance of each sample was evaluated. Table 2 shows the performance evaluation results. The fuel cell stack samples (SA1 to SA8) were manufactured using the "Method for Manufacturing Current Collector Structure 160" described above. The thickness of the Ni foil was set to 50 μm. The processing temperature and processing time of the Ni foil pretreatment process were appropriately changed in order to appropriately change the proportion of grain boundaries with a grain boundary inclination angle of 0° to 40° (the first grain boundary) and grain boundaries with a grain boundary inclination angle of 50° to 90° (the second grain boundary).

[0074] (Calculation of the relative abundance of grain boundaries with a specific grain boundary tilt) For each sample (SA1 to SA8), the abundance ratio of the first grain boundary (grain boundary with a grain boundary inclination angle of 0° or more and 40° or less) and the abundance ratio of the second grain boundary (grain boundary with a grain boundary inclination angle of 50° or more and 90° or less) of the Ni polycrystalline material that constitutes the fuel electrode current collector 144 was calculated using the method described above. To calculate the grain boundary inclination angle, 10 SEM samples were prepared from the current collector structure 160 of each sample. The grain boundaries of the 10 SEM samples were classified into first and second grain boundaries according to the grain boundary inclination angle of each grain boundary. The abundance ratio of the first and second grain boundaries relative to the total number of grain boundaries was calculated. Table 2 shows the abundance ratio of the first and second grain boundaries of the Ni polycrystalline material in each sample (SA1 to SA8). [Table 2]

[0075] (Degradation rate of fuel cell stack 10) For each sample (SA1 to SA8), the degradation rate of the fuel cell stack 10 under continuous operation was determined. Each sample was started at 850°C, and the potential V at the start of operation was measured. I The voltage was measured. Afterward, the temperature was maintained at 850°C and continuous operation was performed. 2000 hours after the start of operation, the potential V after continuous operation was measured. E The following measurements were taken. The degradation rate of the fuel cell stack due to continuous operation of each sample (SA1 to SA8) was calculated using the following formula. Deterioration rate (%)=(V I -V E ) / V I ×100 The degradation rate (%) of the fuel cell stack 10 for each sample is shown in Table 2. Figure 9 is a graph showing the relationship between the abundance ratio of the first grain boundary of the Ni polycrystalline material and the degradation rate for each sample.

[0076] As shown in Table 2 and Figure 9, the samples with a degradation rate of less than 10% were Sample SA1, Sample SA3 to Sample SA8. These samples were equipped with a fuel electrode current collector 144 (Ni polycrystalline) in which the abundance of the first grain boundary was 45% or less. The samples with a degradation rate of less than 8% were Sample SA3 to Sample SA8. These samples were equipped with a fuel electrode current collector 144 in which the abundance of the first grain boundary was 5% or more and 45% or less. The samples with a degradation rate of 3% or less were Sample SA6 to Sample SA8. These samples were equipped with a fuel electrode current collector 144 in which the abundance of the first grain boundary was 5% or more and 45% or less, and the abundance of the second grain boundary was 5% or more and 45% or less.

[0077] (Checking for breakage in sample current collection structure 160) For each sample (SA1 to SA8), the presence or absence of fracture of the current collection structure 160 due to continuous operation was checked. After continuous operation, the samples were disassembled and the current collection structure 160 was removed. When the current collection structure 160 was removed, if the connection between the interconnector 190 and the fuel electrode current collection member 144 was fully maintained, it was determined that there was no fracture of the current collection structure 160. On the other hand, when the current collection structure 160 was removed, if all or part of the fuel electrode current collection member 144 separated from the interconnector 190 at even one point, that is, if the connection between the interconnector 190 and the fuel electrode current collection member 144 was not maintained, it was determined that a fracture of the current collection structure 160 was observed. The presence or absence of fracture of the current collection structure 160 for each sample is shown in Table 2. Note that a + indicates that a fracture of the current collection structure 160 was observed, and a - indicates that no fracture was observed.

[0078] As shown in Table 2, the connection between the interconnector 190 and the fuel electrode current collector 144 was not maintained in sample SA2. Sample SA2 had a fuel electrode current collector 144 in which the proportion of the first grain boundary exceeded 45%. In the other samples (SA1, SA3~SA8), the connection between the interconnector 190 and the fuel electrode current collector 144 was maintained. These samples had fuel electrode current collector 144 in which the proportion of the first grain boundary was 45% or less.

[0079] (Interruption rate of the conductive path of the fuel electrode current collector 144) For each sample (SA1 to SA8), after continuous operation, it was confirmed whether the conductive path of the fuel electrode current collector 144 was blocked. The presence or absence of blockage of the conductive path of the fuel electrode current collector 144 was determined by the following method: The aforementioned SEM samples were subjected to elemental analysis pixel by pixel of the SEM image using an electron probe microanalyzer mounted on the FIB-SEM. Based on the results of the elemental analysis, pixels containing 50% or more of the element Cr among the total elements excluding oxygen were mapped onto the SEM image. The mapped areas were almost entirely Cr2O3. Based on the mapped SEM image, if the surfaces S1 and S2 of the fuel electrode current collector 144 were connected by Cr2O3 and the conductive path was blocked by 99.9% or more, it was determined that the conductive path of the fuel electrode current collector 144 was blocked. The presence or absence of blockage of the conductive path of the fuel electrode current collector 144 was confirmed by taking 10 SEM samples from the current collector structure 160 of each sample and checking each sample. Based on these results, the number of samples in which the conductive path was blocked was divided by the total number of samples for SEM (10 samples) to calculate the conductive path blockage rate (%) for each sample.

[0080] The conductivity path interruption rates for each sample are shown in Table 2. Samples SA2 to SA8 had conductivity path interruption rates of 70% or less. These samples were equipped with fuel electrode current collectors 144 in which the proportion of the first grain boundary was 5% or more. Furthermore, samples SA2, SA5, SA7, and SA8 had conductivity path interruption rates of 50% or less. These samples were equipped with fuel electrode current collectors 144 in which the sum of the proportion of the first grain boundary and the proportion of the second grain boundary was 40% or more.

[0081] From the above results, a fuel cell stack 10 equipped with a fuel electrode current collector 144 (Ni polycrystalline) in which the proportion of first grain boundaries (grain boundaries with a grain boundary inclination angle of 0° to 40°) was adjusted to 5% to 45%, showed suppression of potential degradation and suppression of the conductive path of the fuel electrode current collector 144. In other words, the durability of the fuel cell stack 10 was improved. Furthermore, a fuel cell stack 10 equipped with a fuel electrode current collector 144 (Ni polycrystalline) in which the proportion of second grain boundaries (grain boundaries with a grain boundary inclination angle of 50° to 90°) was adjusted to 5% to 45%, showed further suppression of potential degradation and suppression of the conductive path of the fuel electrode current collector 144. In other words, the durability of the fuel cell stack 10 was further improved.

[0082] B. Variations: The technologies disclosed herein are not limited to the embodiments described above and can be modified in various forms without departing from their essence, for example, the following modifications are possible.

[0083] The materials of each component in the above embodiment are merely examples, and each component may be made of other materials.

[0084] In the above embodiment, a portion of the surface of the interconnector 190, which is a Cr-containing member, may have an oxide film formed on it. The oxide film is mainly composed of, for example, Cr2O3. Furthermore, the proportion of the metal joint portion, which is the portion of the joint area CP where the interconnector 190 and the fuel electrode current collector 144 are joined, where the thickness of the oxide film on the surface of the interconnector 190 is 0.1 μm or less, or where the oxide film is absent, may be 0.0005% or more.

[0085] In the above embodiment, the Ni-containing fuel electrode current collector 144 may contain specific elements at multiple grain boundaries of the Ni polycrystalline material. Furthermore, although the fuel electrode current collector 144 is a Ni foil, it may take other forms. For example, the fuel electrode current collector 144 may be a Ni-containing wire with a diameter of 60 μm or more. The fuel electrode current collector 144 may also be a mesh formed from this wire.

[0086] In the above embodiment, the Cr concentration inside the fuel electrode current collector 144 located near the junction region CP may be 1 atm% or more.

[0087] In the above embodiment, the fuel electrode current collector 144 near the junction region CP of the current collector structure 160 with the interconnector 190 may be porous. Specifically, a region of 5 μm from the surface S2 of the fuel electrode current collector 144 to the interior may be more porous than other regions. The porosity of this porous region may be 5% or more compared to the porosity of other regions.

[0088] In the above embodiment, the method for manufacturing the current collector structure 160 is not limited to the above embodiment. For example, the method for manufacturing the current collector structure 160 may involve assembling the fuel cell stack 10 before the Ni foil pretreatment step, followed by the Ni foil pretreatment step, the bonding step, and the reduction step. Alternatively, the method for manufacturing the current collector structure 160 may involve assembling the fuel cell stack 10 before the bonding step, followed by the bonding step and the reduction step. In this case, the bonding step may involve, for example, treating the fuel cell stack 10 at approximately 850°C for approximately 3 hours. The reduction step may also involve, for example, circulating hydrogen gas through the fuel chamber 323 of the fuel cell stack 10 after the bonding step.

[0089] The configuration of the fuel cell stack 10 and the power generation unit 100U in the above embodiment is merely an example and can be modified in various ways.

[0090] The number of single cells 110 (number of power generation units 100U) included in the fuel cell stack 10 in the above embodiment is merely an example, and the number of single cells 110 is appropriately determined according to the output voltage required for the fuel cell stack 10.

[0091] Although the fuel cell stack 10 in the above embodiment is a co-flow type SOFC, the technologies disclosed herein are also applicable to counter-flow type SOFCs and cross-flow type SOFCs.

[0092] In the above embodiment, the single cell 110 is a fuel electrode-supported single cell, but it may be other types of single cells such as an electrolyte-supported or metal-supported type.

[0093] In the current collection structure 160 of the above embodiment, the interconnector 190 is an example of a Cr-containing member, but the Cr-containing member is not limited to this. For example, if the first plate 232 in the above embodiment contains Cr, the first plate 232 can also be an example of a Cr-containing member, and if the metal support in a metal-supported single cell contains Cr, the metal support can also be an example of a Cr-containing member. Similarly, in the current collection structure 160 of the above embodiment, the fuel electrode current collector member 144 is an example of a Ni-containing member, but the Ni-containing member is not limited to this.

[0094] In the above embodiment, the fuel electrode current collector member 144 of the current collection structure 160 and the fuel electrode 116 of the single cell 110 are connected, but this connection only needs to be electrically connected. Electrically connected here means that the fuel electrode current collector member 144 and the fuel electrode 116 may be directly connected, or they may be connected via, for example, a conductive material.

[0095] In the above embodiment, the fuel cell stack 10 is configured to include a plurality of flat-plate single cells 110, but the technology disclosed herein is equally applicable to fuel cell stacks that include a plurality of other types of single cells (e.g., cylindrical, flat cylindrical, etc.).

[0096] In the above embodiment, the electrochemical reaction cell stack was a cell stack used in a solid oxide fuel cell (SOFC). However, the above configuration is also applicable to cell stacks used in other types of fuel cells such as polymer electrolyte fuel cells (PEFCs), phosphoric acid fuel cells (PAFCs), and molten carbonate fuel cells (MCFCs), or to electrolytic cell stacks that include electrolytic cell units, which are constituent units of solid oxide electrolytic cells (SOECs), as single cells. [Explanation of Symbols]

[0097] 10: Fuel cell stack 100: Power generation block 100U: Power generation unit 110: Single cell 112: Electrolyte layer 114: Air electrode 116: Fuel electrode 118: Reaction prevention layer 120: Separator for single cell 130: Air electrode frame 132: Oxidizer gas supply communication channel 133: Oxidizer gas discharge communication channel 140: Fuel electrode frame 142: Fuel gas supply communication channel 143: Fuel gas discharge communication channel 144: Fuel electrode current collector 149: Spacer 160: Current collector structure 180: Separator for IC 190: Interconnector 191: Flat plate section 192: Air electrode current collector section 193: Coating layer 196: Conductive bonding material 210: First end plate 220: Insulation section 230: End separator 232: First plate 240: First terminal plate 250: Second terminal plate 260: Second plate 270: Second end plate 280: Gas passage member 311: Oxidizer gas supply manifold 312: Oxidizer gas discharge manifold 313: Air chamber 321: Fuel gas supply manifold 322: Fuel gas discharge manifold 323: Fuel chamber CO1: First internal oxide layer CO2: Second internal oxide layer CO: Internal oxide layer CP: Joint area FG: Fuel gas FOG: Fuel off-gas OG: Oxidizer gas OOG: Oxidizer off-gas

Claims

1. A Cr-containing member containing Cr, In an electrochemical reaction cell stack current collector structure comprising a Ni-containing Ni member joined to the Cr-containing member, The Ni-containing member is a polycrystalline material having multiple grain boundaries. Of the aforementioned multiple grain boundaries, the proportion of grain boundaries with a grain boundary inclination angle of 0° or more and 40° or less is 5% or more and 45% or less. A current collection structure for an electrochemical reaction cell stack, characterized by the following features.

2. In the current collector structure for an electrochemical reaction cell stack according to claim 1, Of the aforementioned multiple grain boundaries, the proportion of grain boundaries with a grain boundary inclination angle of 50° or more and 90° or less is between 5% and 45%. A current collection structure for an electrochemical reaction cell stack, characterized by the following features.

3. In the electrochemical reaction cell stack current collection structure according to claim 1 or claim 2, The thickness of the Ni-containing member is 1.5 times or more the average particle diameter of the Ni crystal grains forming the polycrystalline body. Current collection structure for electrochemical reaction cell stacks.

4. A single cell having an electrolyte layer, an air electrode disposed on one side of the electrolyte layer, and a fuel electrode disposed on the other side of the electrolyte layer, A current collector structure for an electrochemical reaction cell stack according to claim 1 or claim 2, comprising: The current collection structure for the electrochemical reaction cell stack and the single cell are electrically connected. Electrochemical reaction cell stack.

5. In the electrochemical reaction cell stack according to claim 4, The Ni-containing member is placed in the fuel chamber that the fuel electrode faces. Electrochemical reaction cell stack.

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